1) Field of the Invention
The present invention relates to expanded structural assemblies and, more particularly, to an expanded structural assembly joined with a plurality of friction weld joints and to preforms and methods for forming such structural assemblies.
2) Description of Related Art
Expanded structural assemblies, and particularly honeycomb panels, are used in a variety of applications in the aerospace industry including, for example, flight control surfaces, acoustic suppression panels, aircraft flooring, other aircraft structural components, and the like. In addition, such expanded structural assemblies are also used in a variety of other industries and applications, including as structural members for automobiles and other vehicles. Honeycomb panels and other expanded structural assemblies advantageously provide a combination of high stiffness and low weight as compared to conventional panels formed from a solid material.
Conventional metal bonded aerospace honeycomb panels are produced by welding or brazing thin “foil like” core sheets to thicker outboard face sheets in a flat configuration. The resulting flat aerospace honeycombs can be used as flat structural panels or further creep-stretch formed into slightly curved shapes.
U.S. Pat. No. 6,537,682 to Colligan, titled “Application of Friction Stir Welding to Superplastically Formed Structural Assemblies,” describes a structural assembly formed by friction stir welding multiple structural members and thereafter superplastically forming the members to form the expanded assembly. The assembly can be formed by inflating the structural members in a die so that the assembly is formed to the shape of the die. The facing surfaces of the structural members can be partially covered with oxide to prevent undesired thermo-compressing welding from occurring adjacent the friction stir weld joints.
Although the methods of the prior art have proven successful in forming expanded structural assemblies, there exists a continued need for an improved expanded structural assembly and methods and preforms for forming the same. Preferably, the method should be capable of forming expanded structural assemblies of various shapes. Further, the structural assemblies should provide consistent expanding of the cells of the assemblies so that the assemblies are formed to the desired shape.